Device for introducing a fluid into a gas stream

ABSTRACT

The present invention relates to a device for introducing a fluid into a gas stream, in particular a reduction agent into an exhaust gas stream of an internal combustion engine. The device has a mixing chamber and a metering device by means of which the fluid can be introduced, via a metering tip, into an injection space defined by a protective sleeve, which injection space is arranged inside the chamber and is fluidically connected to the latter. The protective sleeve has an intermediate chamber which extends in the circumferential direction of the protective sleeve and is bounded radially internally by an inner wall and radially externally by an outer wall, wherein the intermediate chamber is fluidically connected to the injection space via a gap, in particular an annular gap, formed by and at the inner wall. The intermediate chamber is also fluidically connected to the mixing chamber via at least one opening in the outer wall.

The present invention relates to an arrangement for introducing a fluidinto a gas flow, in particular for introducing a reductant into anexhaust gas flow of an internal combustion engine.

The problem of distributing a liquid additive reliably in a suitableform in a gas flow in order, for example, to enable a chemical reactionof components of the gas flow with components of the introduced fluid isone which arises in a number of application areas. This problem arisesin exhaust gas engineering, for example, in connection with the SCRprocess in which an aqueous urea solution is introduced into the exhausttrain of a motor vehicle, for example by means of a metering apparatus.Ammonia and CO₂ are produced from the urea solution by thermolysis andhydrolysis. The ammonia produced in this manner can react in a suitablecatalytic converter with the nitrogen oxides contained in the exhaustgas which are thus efficiently removed from the exhaust gas.

It is of particular relevance in this process that the urea solution isintroduced into the exhaust gas flow in a well-defined form. It ismoreover of great importance that the urea solution introduced into theexhaust gas flow is evaporated as completely as possible and isuniformly distributed in the exhaust gas flow.

In many cases, the urea solution is injected or sprayed into the exhausttrain by a metering apparatus that the exhaust gas flow flows ontoobliquely or laterally. This can have the result that the reductantsprayed in is scattered. The additive introduced frequently forms aspray cone. The latter is deformed by the exhaust gas flow and undercertain circumstances is even urged toward the walls of the exhausttrain. This has the consequence that the injected fluid is distributedless well, which results in a reduction of the efficiency of thecatalysis. In addition, unwanted deposits of the fluid can form in theinterior of the apparatus, in particular also in the region around themetering apparatus, which can likewise result in a reduction of theefficiency or even in a failure of the apparatus or of the exhaust gascleaning system.

It is therefore an object of the present invention to provide anapparatus of the initially named kind having an improved introductionand distribution efficiency of the fluid.

This object is satisfied by an apparatus having the features of claim 1.

In accordance with the invention, the apparatus has a mixing chamber anda metering apparatus. The fluid can be introduced by means of a meteringtip by the metering apparatus into an injection space defined by aprotective sleeve. The injection space is arranged in the interior ofthe chamber and is in fluid communication therewith. The protectivesleeve has an intermediate chamber that extends in the peripheraldirection and that is bounded at the radial inner side by an inner walland at the radial outer side by an outer wall. The intermediate chamberis in fluid communication with the injection space via a gap, inparticular an annular gap, formed by or configured at the inner wall. Onthe other hand, the intermediate chamber is in fluid communication withthe mixing chamber via at least one opening—in particular a plurality ofopenings—in the outer wall.

In other words, the fluid is introduced into the injection space definedby the protective sleeve by means of the metering tip of the meteringapparatus. The injection space is open toward the mixing chamber. Theprotective sleeve thus forms a kind of screen that prevents the gas fromflowing directly onto the metering tip. The protective sleeve—at leastinitially—also protects the spray cone, which results in a betterdistribution of the fluid in the gas flow.

In addition, the protective sleeve acts as a kind of “flushingapparatus” to protect the metering tip from the formation of deposits bybeing flowed around by gas. Some of the gas flowing onto the protectivesleeve can namely penetrate into the intermediate chamber through theopenings in the outer wall of the protective sleeve. The gas flows fromsaid intermediate chamber into the injection space through the gapforming a constricted opening. The exhaust gas flowing through the gapinto the injection space can be guided in this respect such that it atleast largely prevents the formation of deposits in the region of theinjection space and in particular of the metering tip.

Further embodiments of the invention are set forth in the description,in the dependent claims and in the enclosed drawings.

In accordance with an embodiment, the gap surrounds the metering tip atleast partly, preferably completely, in the peripheral direction. Thegap is in particular arranged such that at least some of the gas flowflowing therethrough flushes behind the metering tip. For this purpose,the gap can be arranged—viewed in the axial direction, i.e. in thedirection of introduction of the fluid—approximately at the level of themetering tip or even in front of it.

At least one guide element can be arranged in the gap and a swirlcomponent can be imparted through said gap to at least some of the gasflow flowing therethrough. Such a flow eddy can contribute to preventingthe formation of deposits even more efficiently. In addition, the swirlprovides that the flow follows a contour of the inner wall defining theinjection space better so that flow separations are minimized.

In accordance with a further embodiment of the apparatus in accordancewith the invention, a part of a wall of the mixing chamber at leastsectionally bounds the intermediate chamber. It in particular bounds itin the region around the metering tip. The protective sleeve can, forexample, be fastened to the wall of the mixing chamber, in particularvia its outer wall, so that the wall of the mixing chamber and the innerand outer walls of the protective sleeve together define theintermediate chamber. It is, however, also possible to at leastsectionally bound an end of the intermediate chamber facing the meteringtip by a base section of the protective sleeve. The base section of theprotective sleeve is in particular connected to the outer wall or isformed in one piece therewith. The base section can be arranged spacedapart from the wall of the mixing chamber. A flow path is therebyestablished between the protective sleeve and the mixing chamber walland contributes to an (additional) flowing behind of the metering tip tofurther reduce the formation of deposits.

The gap can be bounded by an end section of the inner wall facing themetering tip, by a part of a wall of the mixing chamber sectionallybounding the intermediate chamber and/or—if provided—by the base sectionof the protective sleeve. The inner wall is in particular provided witha collar at its end facing the metering tip, said collar projecting intothe intermediate chamber to efficiently guide the gas flow through thegap. I.e. in an embodiment of the apparatus in accordance with theinvention, the end section of the inner wall of the sleeve—with orwithout a collar—is spaced apart from the wall of the mixing chamber orfrom the base section to form the gap.

The at least one opening in the outer wall can be a bore, an elongatehole and/or a slit. A plurality of openings are in particular providedthat are preferably evenly distributed in the peripheral direction.Provision can, however, also be made for specific applications toprovide larger, differently shaped and/or more openings in specificregions of the outer wall, for example to compensate an uneven onflowonto the protective sleeve by the gas flow. Openings having differentshapes can also be combined.

In accordance with an embodiment, the inner wall has a funnel-like orconical section that opens in a direction away from the metering tip.I.e. the named section diverges in the direction of introduction of thefluid to take account of its “development”. The inner wall is inparticular configured without interruption so that the gas can onlyenter into the injection space from the intermediate chamber through thegap.

Alternatively or additionally, the outer wall can also have afunnel-like or conical section that opens in a direction toward themetering tip. I.e. in this embodiment, the named section converges inthe direction of introduction of the fluid.

In accordance with an embodiment of the protective sleeve, it is formedin one piece. Alternatively, the inner wall and the outer wall of theprotective sleeve can be separately manufactured elements that areconnected to one another, in particular welded or soldered to oneanother. The connection between the inner wall and the outer wall can beprovided at their ends remote form the metering tip, for example.

In accordance with an inexpensive embodiment of the protective sleevethat is also suitable for many application cases, the protective sleeveis substantially rotationally symmetrical. To take account of specialflow conditions, however, an asymmetrical design can also be provided.

The mixing chamber can have at least one inlet opening that is arrangedand configured such that the protective sleeve, in particular its outerwall, is flowed onto by at least some of the gas flow flowing into themixing chamber. An at least partly radial, oblique and/or lateral onflowof the protective sleeve can in particular be present.

A plurality of inlet openings can, however, also be provided that arearranged around the protective sleeve. At least one opening, inparticular exactly one opening, in the outer wall of the protectivesleeve can be associated with each of the inlet openings.

A gas guidance element that guides at least some of the gas flow towardthe protective sleeve can be arranged in the mixing chamber. The gasguidance element can be connected to the protective sleeve and canproject into the gas flow flowing onto the protective sleeve. Anupstream end of the gas guidance element is in particular arrangedsubstantially in parallel with the gas flow to prevent the generation ofunnecessary eddies.

The gas conductance element can generally be a separate componentthat—as mentioned above—is connected, or is also not connected, to theprotective sleeve. The gas conductance element can, however, also beformed by a section of the outer wall of the protective sleeve. Inaccordance with an embodiment, the gas conductance element is associatedwith at least one opening in the outer wall of the protective sleeve toguide some of the gas flow into or through the opening so that it entersinto the intermediate chamber. The gas conductance element is inparticular arranged in the region of the opening. The gas conductanceelement is, for example, formed at least in part by a section of theouter wall of the protective sleeve that was bent out, for example, toform the at least one opening in the outer wall.

The gas conductance element can have a section that is formed in U shapeor that has the form of an incomplete U. It is e.g. conceivable that thegas conductance element is bent out of the outer wall so that it mergesinto the outer wall in a bend. In the further course, the gasconductance element can be correspondingly shaped to guide a desiredpart proportion of the gas flow into the intermediate chamber.

The gas conductance element can comprise openings, e.g. holes. Theopenings are in particular arranged in a region that is arrangedadjacent to the protective sleeve.

The gas conductance element can project into an inlet opening of themixing chamber or can even project through it to optimize the gas flow.

In accordance with a further embodiment of the present invention, themixing chamber has a bypass flow path through which the at least some ofthe gas flow flows into or through the mixing chamber without flowingonto the protective sleeve or even flowing through the protectivesleeve, in particular its intermediate chamber. The bypass flow path is,for example, at least sectionally defined by a wall of the mixingchamber and by an end of the protective sleeve remote from the meteringtip.

The wall of the mixing chamber can have an inwardly directed bead thatis arranged approximately at the level of the protective sleeve in theaxial direction of the mixing chamber to optimize the onflow of theprotective sleeve.

A gas guidance pipe whose outer periphery is arranged spaced apart fromthe wall of the mixing chamber can be arranged in the mixing chamber forthe additional protection of the spray cone—spray-in geometriesdiffering from a conical shape are also conceivable. The wall of themixer chamber and the outer periphery of the gas guidance pipe thussectionally define a gap through which gas can flow. The gas guidancepipe is in particular arranged downstream of the metering apparatus.

At least one flow conductance element can be arranged in the gap betweenthe wall of the mixer chamber and the gas conductance pipe to impart awell-defined flow pattern on the gas flowing through the gap. A swirl isin particular imparted on the gas flow by a flow conductance element orpreferably by a plurality of flow conductance elements arrangeddistributed in the peripheral direction of the gap. The flow conductanceelement or elements is/are in particular arranged at the inlet side ofthe gap.

In accordance with an embodiment, at least one flow conductance elementis arranged in the gas conductance pipe. This means that, in anembodiment, at least one flow conductance element at least partlyprojects into the gas conductance pipe or is completely arrangedtherein. A flow conductance element that at least sectionally projectsinto the gas conductance pipe and/or is connected to the inner peripheryof the gas conductance pipe is in particular provided at the inlet-sideend of the gas conductance pipe. A plurality of flow conductanceelements are preferably provided.

The at least one flow conductance element can be arranged between theprotective sleeve and the gas conductance pipe. In other words, the atleast one flow conductance element is arranged at least sectionally inan intermediate space or gap between the protective sleeve and the gasconductance pipe. A plurality of flow conductance elements arepreferably provided that impart a swirl on the gas flow that flows intothe gas conductance pipe through the intermediate space or gap betweenthe protective sleeve and the gas conductance pipe. The at least oneflow conductance element is in particular arranged between a downstreamsection of the protective sleeve and an upstream section of the gasconductance pipe. The flow conductance element can be in contact with oreven connected to the gas conductance pipe and/or to the protectivesleeve.

The protective sleeve can project at least sectionally into the gasconductance pipe in the axial direction. Laterally onflowing gas cantherefore not flow directly onto the injected fluid.

The gas conductance pipe can have a section that flares in the flowdirection of the gas flow. In accordance with an embodiment, the gasconductance pipe has a funnel-like inlet region and/or a constrictionhaving a reduced cross-section. The gas flowing into the gas conductancepipe and the injected fluid are efficiently “captured” by thefunnel-like inlet region. The optionally provided constriction generatesan advantageous nozzle effect that increases the efficiency of theapparatus in accordance with the invention. To take account of theconstruction space circumstances, the gas conductance pipe can also havea curved section.

The gas conductance pipe can in particular be arranged coaxially to themixing chamber and/or protective sleeve.

The mixing chamber is in particular a tubular section of an exhaust gassystem.

The invention will be explained in the following purely by way ofexample with reference to advantageous embodiments and to the encloseddrawings. There are shown:

FIG. 1 a first embodiment of the apparatus in accordance with theinvention;

FIGS. 2 to 5 an embodiment of the protective sleeve;

FIGS. 6 and 6 a a sectional view and a side view respectively of afurther embodiment of the apparatus in accordance with the invention;

FIG. 7 a sectional view of a further embodiment of the apparatus inaccordance with the invention;

FIGS. 8 to 11 different views of the protective sleeve with a gasconductance element fastened thereto of the embodiment of the apparatusin accordance with the invention shown in FIGS. 6 and 6 a;

FIGS. 12 to 15 further embodiments of the protective sleeve;

FIG. 16 a further embodiment of the apparatus in accordance with theinvention in a sectional view;

FIG. 17 a further embodiment of the protective sleeve; and

FIGS. 18 and 19 a sectional view and plan view respectively of theprotective sleeve in accordance with FIG. 17 in its installationposition.

FIG. 1 shows a first embodiment 10 of the apparatus in accordance withthe invention for introducing a fluid into a gas flow. In the specificapplication, the apparatus is integrated into an exhaust train of amotor vehicle. The exhaust gas expelled by its internal combustionengine flows through an exhaust pipe 12 through an inlet opening 14 intoa mixer pipe 16. The mixer pipe 16 is in turn connected to downstreamcomponents of the exhaust gas system that are not shown, however. Ametering apparatus for introducing the reductant into the exhaust gasflow is fastened to a base section 18 of the mixer pipe 16. Only ametering tip 20 of the metering apparatus that projects into the mixerpipe 16 can be recognized in FIG. 1. The metering tip 20 is protected bya protective sleeve 22 from being flowed onto directly by the exhaustgas flowing through the inlet opening 14. If the protective sleeve 22were not present, a spray cone 24 of the reductant, shown dashed, wouldpractically be deformed directly after the exit from the metering tip 20by the exhaust gas flowing into the mixer pipe 16. In other words, thefluid sprayed in would be urged toward the side of the mixer pipe 16 atthe left in FIG. 1, whereby the fluid in the exhaust gas flow would bedistributed unevenly and whereby unwanted deposits of the reductantcould even occur at the inner wall of the mixer pipe 16.

The protective sleeve 22 comprises an outer wall 26 that is connected,in particular welded or soldered, to the base section 18 (e.g.deflection shell) of the mixer pipe 16. The outer wall 26 has openings28 through which some of the exhaust gas flowing onto the protectivesleeve 22 can enter into an intermediate chamber 30 that is bounded bythe outer wall 26 and by an inner wall 32 opening conically in adirection away from the metering tip 20. The inner wall 32 and the outerwall 26 are indirectly connected to one another via an end face section34. A direction connection of the walls 26, 32 is likewise conceivable.The inner wall 32 and the outer wall 26 as well as the end face section34—if present—are in particular formed in one piece. Provision can,however, also be made to manufacture the inner wall 32 and the outerwall separately from one another and then to connect them to oneanother, in particular at their ends remote from the metering tip 20.

The substantially funnel-like inner wall 32 defines an injection space36 which is open toward the interior of the mixer pipe 16 and in whichthe spray cone 24 which is generated by the metering tip 20 is protectedfrom a direct onflow by the exhaust gas.

To prevent the formation of reductant deposits in the region of themetering tip 20, provision is made to flush behind it in a well-definedform. The flushing behind has to be sufficiently efficient, on the onehand, and, on the other hand, an impairment of the development of thespray cone 24 should be avoided as much as possible.

The exhaust gas flowing into the intermediate chamber 30 is used forthis purpose. An annular gap 38 that represents a constricted openingfor exhaust gas flowing out of the intermediate chamber 30 into theinjection space 36 is formed between the base section 18 and the end ofthe inner wall 32 facing the metering tip 20.

As is indicated by flow paths 40, at least some of the exhaust gasflowing laterally onto the protective sleeve 22 flows through theopenings 28 into the intermediate chamber 30. Some of the exhaust gasalso flows around the protective sleeve 22 and enters into theintermediate chamber 30 at sides of the protective sleeve 22 not facingthe inlet opening 14. Substantially homogeneous pressure conditions arepresent in the intermediate chamber 30 in an operation of the exhaustgas system. The exhaust gas moves out of the intermediate chamber 30through the gap 38 into the injection space 36. A flow through the gap38 that is also substantially homogeneous in the peripheral direction isformed due to the homogeneous pressure conditions in the chamber 30. Thepositioning of the gap 38 ensures that the metering tip 20 is flowedaround by exhaust gas so that no deposits of the reductant can be formedhere.

The protective sleeve 22 acts—in functional terms—approximately as atwo-stage restriction apparatus. The first restriction takes place onthe flowing of the exhaust gas through the openings 28 into theintermediate chamber 30. The second restriction is achieved by the gap38. It is thereby ensured that well-defined flow conditions and pressureconditions that reliably prevent the formation of deposits are presentin the region around the metering tip 20. Since the inner wall 32 isformed without interruption, the spray cone 24 is also not disturbed bygas inflowing in the radial direction—apart from the region around thegap 38. The exhaust gas passing through the gap 38 follows the geometryof the inner wall 32 in the injection space 36 and therefore has mainlyaxial flow components.

To design the inflow of the exhaust gas out of the intermediate chamber30 into the injection space 36 as free of eddies as possible, the end ofthe inner wall 32 facing the metering tip 20 is provided with a curvedcollar 42 that extends into the intermediate chamber 30.

However, the total exhaust gas that enters into the mixer pipe 16through the inlet opening 14 does not flow around or even through theprotective sleeve 22. Some of the exhaust gas—marked by flow paths40′—flows between the end of the protective sleeve 22 remote from themetering tip 20 and the right hand lower outer wall of the mixer pipe 16directly into said mixer pipe. The flow paths 40′ thus symbolize abypass flow. It is understood that the bypass flow depends inter alia onthe dimensioning of the protective sleeve 22 and of the mixer pipe 16.It is by all means conceivable that the protective sleeve 22 has asmaller axial extent than shown in FIG. 1 or even extends even furtherinto the mixer pipe 16, which signifies less or more protectionrespectively for the spray cone 24. The conditions for a distribution ofthe reductant that is as good as possible can be set by the dimensioningof the named components 22, 16. The same also applies to the geometricaldesign of the walls 26, 32 of the protective sleeve 22 and of theopenings 28 and of the gap 38 while taking account of the geometry ofthe spray characteristics/spray geometry of the metering apparatus.

FIGS. 2 to 5 show different views of a further embodiment 22 a of theprotective sleeve (side view, sectional view, plan view or perspectiveview). Unlike with the protective sleeve 22 that has a substantiallycylindrical outer wall 26, the outer wall 26 of the protective sleeve 22a is shaped slightly conically. The outer wall 26 is provided withelongate holes 44 that are evenly distributed in the peripheraldirection. The outer wall 26 is provided at its end facing the meteringtip 20 in the installation position with a flange section 46 tofacilitate the fastening of the protective sleeve 22 a to the basesection 18 of the mixer pipe 16.

The inner wall 32 of the protective sleeve 22 a is formed in funnelshape (see in particular FIG. 3) and has a curved shape that merges atthe metering tip side into a collar 42 optimizing the flow through thegap 38. The inner wall 32 merges into the outer wall 26 by a curvatureat the side remote from the metering tip 20. It can clearly berecognized (cf. FIG. 3) that the protective sleeve 22 a is asingle-piece sheet metal component.

FIGS. 6 and 6 a show a further embodiment 10′ of the apparatus inaccordance with the invention. The apparatus 10′ is connected in onepiece to an inlet stub 48 and to an outlet stub 50 that make theconnection to the further components of the exhaust gas system possible.

To guide the exhaust gas entering into the mixer pipe 16 through theinlet opening 14 toward the protective sleeve, that is here formed as afurther embodiment 22 b, in a well-defined manner, it comprises a gasconductance element 52. The gas conductance element 52 is also shown indifferent views in FIGS. 8 to 11. It substantially comprises atongue-shaped metal sheet that is connected at about half height to theouter wall 26 of the protective sleeve 22 b. The gas conductance element52 projects in the installation position through the inlet opening 14into the inlet stub 48. An upstream end 54 of the gas conductanceelement 52 is arranged and configured such that it is alignedsubstantially in parallel with the onflowing gas flow. Disadvantageouseddying at the upstream end 54 is thus avoided.

The gas flow flowing onto the apparatus 10′ is split into two part flowsby the gas conductance element 52. A first part flow flows beneath thegas conductance element 52 onto the protective sleeve 22 b. The outerwall 26 of the protective sleeve 22 b is provided with circular holes44′ in the region flowed onto by the first part flow so that thisportion of the gas flow can enter into the intermediate chamber 30. Theexhaust gas flows from there through the gap 38 into the injection space36 and in so doing flushes behind the metering tip 20 of the meteringapparatus (not shown) that is fastened via a fastening flange 55 to thebase section 18 in a gas tight manner.

The second part flow flows above the gas conductance element 52 toward asection of the protective sleeve 22 b that is free of interruption. I.e.this portion of the exhaust gas cannot enter into the intermediatechamber 30, but rather flows into the pipe 58 through an annular gap 56between a gas conductance pipe 58 arranged in the mixer pipe 16 and theend of the protective sleeve 22 b remote from the metering tip. Sincethe protective sleeve 22 b projects in the axial direction into the endof the gas conductance pipe 58 facing the metering tip 20, no exhaustgas can flow directly into the gas conductance pipe 58, but it mustrather “force” itself through the gap 56. It is thereby effected thatthe exhaust gas originally onflowing obliquely or laterally has asubstantially axial flow direction in the interior of the gasconductance pipe 58, which contributes to a further protection of thespray cone 24 and thus assists the uniform distribution of the reductantin the exhaust gas flow.

The portion of the second part flow not flowing onto the protectivesleeve 22 b impacts the outer wall of the end of the gas conductancepipe 58 facing the protective sleeve 22′ and flows through a bypass gap60 that is formed by the outer wall of the gas conductance pipe 58 andby the inner wall of the mixer pipe 16 spaced apart therefrom. Thisportion of the exhaust gas flow thus does not come into contact with theprotective sleeve 22 b.

The protective sleeve 22 b and the gas conductance pipe 58 are alignedcoaxially to the mixer pipe 16.

FIG. 6a shows a side view of the apparatus 10′, whereby the fasteningflange 55 for the metering apparatus can be clearly recognized.

FIG. 7 shows an embodiment 10′″ of the apparatus in accordance with theinvention that corresponds in most aspects to the apparatus 10′ of FIGS.6 and 6 a. Additional flow conductance elements 59, 59′ are, however,provided to optimize the gas flow through the apparatus 10′″.

The flow conductance elements 59 are arranged in the bypass gap 60, moreprecisely in its inlet region. The flow conductance elements 59 that inparticular have surface sections that are angled, curved and/or planarwith respect to the main flow direction impart a swirl-like flow patternonto the gas flow flowing into the bypass gap 60 in the embodiment 10′″.It is thereby achieved that the gas conductance pipe 58 is—in simplifiedterms—spirally flowed around. It is understood that the number,arrangement and/or design of the flow conductance elements 59 is/arefreely selectable to generate the flow pattern (with or without a swirlcomponent) suitable for the respective application.

The flow conductance elements 59′ span the annular gap 56 between thegas conductance pipe 58 and the end of the protective sleeve 22 b remotefrom the metering tip. The flow conductance elements 59′ are alsoprovided in the apparatus 10′″ to generate a swirl-like flow pattern.I.e. the exhaust gas flowing into the gas conductance pipe 58 throughthe annular gap 56 has a flow pattern acted on by swirl. It also applieshere that the number, design and/or arrangement of the flow conductanceelements 59′ can be adapted to the respective circumstances present togenerate the respective desired flow pattern. In the apparatus 10′″shown by way of example, the flow conductance elements 59′ extend overthe total annular gap 56. However, they only project partly into thepipe 58. The flow conductance elements 59′ are in contact with theupstream end section of the gas conductance pipe 58, on the one hand,and with a downstream section of the protective sleeve 22 b, on theother hand. The flow conductance elements 59′ can be fixedly connectedto the components 58, 22 b. It is, however, also possible that the flowconductance elements 59′ only extend over a part of the annular gap 56.The same naturally applies analogously to the flow conductance elements59.

FIG. 8 shows a cross-section through the protective sleeve 22 b with thegas conductance element 52. Both components 22 b, 52 are sheet metalparts. They have been connected to one another, for example by weldingor soldering. The protective sleeve 22 b has an outer wall 26 shapedmore conically than the protective sleeve 22 a. The inner wall 32 of theprotective sleeve 22 b forms a funnel extended a little longer than theinner wall 32 of the protective sleeve 22 a. The inner wall 32 is,however, likewise slightly curved. The collar 42 of the protectivesleeve 22 b, in contrast to the collar 42 of the protective sleeve 22 a,has a smaller curvature. This illustrates that the geometry of theprotective sleeve can be varied to a wide extent to meet the respectivedemands.

It becomes clear from a joint review of FIGS. 6 to 11 that the metal gasconductance sheet 52 practically completely terminates an end section ofthe mixer pipe 16 facing the metering apparatus to ensure that theportion of the exhaust gas flowing into this section is provided ascompletely as possible for the flushing behind of the metering tip 20.Which exhaust gas quantities are provided for flushing behind themetering tip can thus be exactly fixed by the gas conductance element52, i.e. by its arrangement and formation.

FIG. 12 shows an embodiment 22 c of the protective sleeve. However, ithas a base section 62 in addition to the walls 26, 32 that is formed inone piece with the wall 26 or that is manufactured separately therefromand was subsequently connected to it. The base section 62 has an openingassociated with the metering tip 20 to enable the injection of thereductant into the injection space 36. It is ensured by means of spacers64 that the base section 62 is arranged spaced apart from the basesection 18 of the mixer pipe 16. A flush-behind gap 66 is therebygenerated through which a flow path 40″ leads. The exhaust gas flowingthrough the gap 66 contributes to the flushing behind of the meteringtip 20. It is a purpose of this aspect of the flushing behind to branchoff a suitably large mass flow that ensures a good flushing, on the onehand, but that is also not too large, on the other hand. The heat inputin the region of the metering tip 20 should namely not exceed a specificlimit value.

FIG. 13 shows a further embodiment 22 d of the protective sleeve. It hasboth a curved inner wall 32 and an outer wall 26 formed as curved togenerate the desired flow pattern. Openings 28 are provided at the rightpart of the outer wall to enable the entry of gas into the intermediatechamber 30. The outer wall 26 has no openings 28 at the left side of theprotective sleeve 22 d. It is, however, provided with an outer wallsection 68 that—in a similar manner to the gas conductance element 52 ofthe protective sleeve 22 b-projects through the inlet opening 14 intothe inlet stub 48. A portion of the exhaust gas can thus move directlyinto the intermediate chamber 30 (cf. flow path 40′″).

To optimize the flow conditions, the wall of the mixer pipe 16 isprovided in the region of the protective sleeve 22 d with a bead 70whose design varies in the peripheral direction. Depending on the axialposition—in particular when the bead 70 is above the inlet opening 14 inthe axial direction—it can also have a constant design in the peripheraldirection.

FIGS. 14 and 15 show a further embodiment 22 e of the protective sleeve(only one opening 28 shown in FIG. 15). It has conical inner and outerwalls 32, 26. Guide elements 72 through which a swirl component isimparted onto the exhaust gas flowing through the gap 38, as the flowpath 40″″ indicates by way of example, are arranged in the gap 38between the collar 42 of the inner wall 32 at the meter tip side and thebase section 18 of the mixer pipe 16. This measure also produces abetter flushing behind of the metering tip 20 and a more efficientdistribution of the reductant in the exhaust gas flow. In addition, thismeasure makes possible larger angles at the cone without having to feara separation of the flow.

FIG. 16 shows a further embodiment 10″ of the apparatus in accordancewith the invention. The apparatus 10″ shows a very similar design to theapparatus 10′ with respect to the design of the mixer pipe 16 (cf. FIGS.6 and 7). However, the protective sleeve 22 f differs from theprotective sleeve 22 in that guide elements 72 are provided that guidethe exhaust gas located in the intermediate chamber 30 toward the gap 38and in so doing impart a swirl onto the exhaust gas. Unlike the guideelements 72 of FIGS. 14 and 15, the guide elements 72 of the protectivesleeve 22 f are outwardly curved so that they project into theintermediate chamber 30.

The fastening flange 55 shown in FIGS. 6 and 7 was not shown to increasethe clarity in FIG. 16. It is, however, clear that the fastening of themetering apparatus can take place in the same manner or in a similarmanner to that of the apparatus 10′.

A further difference between the apparatus 10′ and 10″ is that a gasconductance pipe 58′ of the apparatus 10 has a somewhat different designthan the gas conductance pipe 58. The gas conductance pipe 58′ has afunnel-like inlet region 74 into which the end (end face section 34) ofthe protective sleeve 26 f remote from the metering tip 20 projects. Anopening plane of the funnel-like inlet region 74 is in this respect notin parallel with a plane defined by the margin of the protective sleeve26 f remote from the metering tip 20.

A constriction 76 that develops a nozzle effect adjoins the funnel-likeinlet region 74 by which the efficiency of the apparatus 10″ isincreased.

The gas conductance pipe 58′ additionally extends further into the mixerpipe 16 than the mixer pipe 58. In this respect, it substantiallyfollows a downstream geometry of the mixer pipe 16 so that it has acurved section 78.

A gas conductance element 52′ of the apparatus 10″ is likewise of asomewhat different design than the gas conductance element 52 of theapparatus 10′. It not only projects into the inlet stub 48, but evenextends into a pipe 80 connected to the inlet stub 48. The gasconductance element 52′ in this respect follows the geometry of the pipe80 so that the upstream end 54 of the gas conductance element 52′ isarranged in parallel with the main flow direction of the exhaust gas inthe pipe 80. The gas conductance element 52, 52′ can also be formed asmulti-piece e.g. can comprise components plugged into one another orconnected to one another with material continuity.

Unlike the gas conductance element 52, the gas conductance element 52′additionally has holes 44″. They are arranged in a region adjacent tothe protective sleeve 22 f and allow a passage of exhaust gas in thisregion.

The design of the gas conductance element 52′ provides an earlyseparation of the exhaust gas flow into a portion that is guided towarda lower section of the protective sleeve 22 f and into a portion that isguided toward the upper part of the protective sleeve 22 f or to thebypass gap 60. Due to the constriction 76 and due to the geometry of thefunnel-like inlet region 74, the bypass gap 60 has a fluid mechanicallymore favorable design of the entry region than the gap 60 of theapparatus.

FIG. 17 shows a protective sleeve 22 g that has tabs 82 forming flowconductance elements. The tabs 82 are each associated with a gap opening84. I.e. each tab 82 guides the gas flowing onto it toward a specificgap opening 84. The tabs 82 can be obtained, for example, in thatincisions are made in the outer wall 26 and the tabs 82 are subsequentlybent out.

FIGS. 18 and 19 show the protective sleeve 22 g in its installationposition. The protective sleeve 22 g has—as can be easily seen in thesection of FIG. 18—an inner wall 32 without interruption that opens atthe metering tip side into a collar 42 projecting into the intermediatechamber 30. The collar 42 together with the base section 18 defines thegap 38. The base section 18 is arranged a little lowered relative toinlet stubs 48 that open into the mixer pipe 16. It is a componentseparate from the pipe 16, but connected thereto in a gas tight manner.

To guide exhaust gas flowing through the respective inlet opening 14 ofthe stubs 48 at least partly toward the gap openings 84, the tabs 82 arecorrespondingly curved or bent. FIG. 18 shows that four stubs 48connected to exhaust pipes 12 open into the mixer pipe 16. A respectivegap opening 84 is associated with each stub 48 and thus with each inletopening 14. A respective tab 82 is in turn associated with each gapopening 84 and an exactly defined proportion of the exhaust gas flowinginto the mixer pipe 16 can be conducted therethrough into theintermediate chamber 30.

It is understood that individual features that have been described inconnection with specific embodiments of the protective sleeve can befreely combined to obtain a design of the protective sleeve that isoptimum for the respective conditions present. It is generally alsopossible to provide openings at the end face of the protective sleeveremote from the metering tip so that exhaust gas can also flow out ofthe intermediate chamber in the axial direction. The constriction sleevecan be actively heated to evaporate reductant impacting it even faster,in particular when the exhaust flow has not yet led to the heating ofthe components of the apparatus in accordance with the invention (e.g.briefly after starting the engine). The surface of the protective sleevecan also be catalytically coated.

The gap forming a constricted opening to establish a fluid communicationbetween the intermediate chamber and the injection space can have adesign varying in the peripheral direction (e.g. a varying gap width).It is, however, preferred to configure the gap in as constant a manneras possible in the peripheral direction to enable a flow of the gas intothe injection space that is homogeneous in the peripheral direction.

The concept in accordance with the invention of first enabling an entryof the exhaust gas into an intermediate chamber through openings in theouter wall of the protective sleeve and only subsequently to utilize theexhaust gas to flow behind the metering tip leads to much smallerdeposits than with previously known concepts. A substantially evenpressure level is namely formed in the intermediate chamber so that thethroughflow of the gap and thus the flowing behind of the metering tipare likewise comparatively homogeneous. The exhaust gas flowing throughthe gap additionally flushes the reductant out of the injection space. Amore homogeneous distribution of the reductant in the exhaust gasresults overall.

REFERENCE NUMERAL LIST

-   10, 10′, 10″, 10′″ apparatus-   12 exhaust pipe-   14 inlet opening-   16 mixer pipe-   18 base section-   20 metering tip-   22, 22 a, 22 b,-   22 c, 22 d, 22 e,-   22 f, 22 g protective sleeve-   24 spray cone-   26 outer wall-   28 opening-   30 intermediate chamber-   32 inner wall-   34 end face section-   36 injection space-   38 gap-   40, 40′, 40″,-   40′″, 40″ flow path-   42 collar-   44, 44′, 44″ hole-   46 flange section-   48 inlet stub-   50 outlet stub-   52, 52′ gas conductance element-   54 upstream end-   55 fastening flange-   56 annular gap-   58, 58′ gas conductance pipe-   59, 59′ flow conductance element-   60 bypass gap-   62 base section-   64 spacer-   66 back-flushing gap-   68 outer wall section-   70 bead-   72 guide element-   74 funnel-like inlet region-   76 constriction-   78 curved section-   80 pipe-   82 tab-   84 gap opening

1-35. (canceled)
 36. An apparatus for introducing a fluid into a gasflow, the apparatus having a mixing chamber and having a meteringapparatus through which the fluid can be introduced by means of ametering tip into an injection space, the injection space being definedby a protective sleeve in a radial direction, the injection space beingarranged in the interior of the mixing chamber, and the injection spacebeing in fluid communication with the mixing chamber, wherein theprotective sleeve has an intermediate chamber that extends in theperipheral direction of the protective sleeve, the intermediate chamberbeing bounded at the radially inner side by an inner wall and at theradially outer side by an outer wall, with the intermediate chamberbeing in fluid communication with the injection space via one of a gapformed by the inner wall and a gap configured at the inner wall and theintermediate chamber being in fluid communication with the mixingchamber via at least one opening in the outer wall.
 37. The apparatus inaccordance with claim 36, wherein the gap at least partly or completelysurrounds the metering tip in the peripheral direction.
 38. Theapparatus in accordance with claim 36, wherein the gap is arranged suchthat at least some of the gas flow flowing therethrough flushes behindthe metering tip.
 39. The apparatus in accordance with claim 36, whereinat least one guide element is arranged in the gap and a swirl componentcan be imparted through said gap onto at least some of the gas flowflowing therethrough.
 40. The apparatus in accordance with claim 36,wherein a part of a wall of the mixing chamber at least sectionallybounds the intermediate chamber.
 41. The apparatus in accordance withclaim 36, wherein an end of the intermediate chamber facing the meteringtip is at least sectionally bounded by a base section of the protectivesleeve.
 42. The apparatus in accordance with claim 41, wherein the basesection is arranged spaced apart from a wall of the mixing chamber. 43.The apparatus in accordance with claim 36, wherein the gap is bounded byan end section of the inner wall facing the metering tip, by a part of awall of the mixing chamber sectionally bounding the intermediate chamberand/or by the base section.
 44. The apparatus in accordance with claim36, wherein the inner wall is provided at its end facing the meteringtip with a collar that projects into the intermediate chamber.
 45. Theapparatus in accordance with claim 36, wherein the at least one openingin the outer wall is a bore, an elongate hole and/or a slit.
 46. Theapparatus in accordance with claim 36, wherein the inner wall has afunnel-like or conical section that opens in a direction away from themetering tip.
 47. The apparatus in accordance with claim 36, wherein theinner wall is formed without interruption.
 48. The apparatus inaccordance with claim 36, wherein the outer wall has a funnel-like orconical section that opens in a direction facing the metering tip. 49.The apparatus in accordance with claim 36, wherein the protective sleeveis formed in one piece.
 50. The apparatus in accordance with claim 36,wherein the outer wall and the inner wall of the protective sleeve areseparate elements that are connected to one another.
 51. The apparatusin accordance with claim 36, wherein the protective sleeve issubstantially rotationally symmetrical.
 52. The apparatus in accordancewith claim 36, wherein the mixing chamber has at least one inlet openingthat is arranged and configured such that the protective sleeve isflowed on by at least some of the gas flow flowing into the mixingchamber.
 53. The apparatus in accordance with claim 52, wherein arespective at least one opening in the outer wall is associated witheach inlet opening.
 54. The apparatus in accordance with claim 36,wherein a gas conductance element that guides at least some of the gasflow toward the protective sleeve is arranged in the mixing chamber. 55.The apparatus in accordance with claim 54, wherein the gas conductanceelement is connected to the protective sleeve and projects into the gasflow flowing onto the protective sleeve.
 56. The apparatus in accordancewith claim 55, wherein the gas conductance element is associated with atleast one opening to guide a portion of the gas flow into the opening.57. The apparatus in accordance with claim 54, wherein the gasconductance element has a section that is configured in U shape or hasthe form of a complete U.
 58. The apparatus in accordance with claim 54,wherein the gas conductance element is at least partly formed by asection of the outer wall of the protective sleeve.
 59. The apparatus inaccordance with claim 54, wherein the gas conductance element projectsinto an inlet opening of the mixing chamber or therethrough.
 60. Theapparatus in accordance with claim 36, wherein the mixing chamber has abypass flow path through which at least some of the gas flow flows intoor through the mixing chamber without flowing onto the protective sleeveor without flowing through the protective sleeve.
 61. The apparatus inaccordance with claim 60, wherein the bypass flow path is at leastsectionally defined by a wall of the mixing chamber and by an end of theprotective sleeve remote from the metering tip.
 62. The apparatus inaccordance with claim 36, wherein the wall of the mixing chamber has aninwardly directed bead that is arranged approximately at the level ofthe protective sleeve in the axial direction of the mixing chamber. 63.The apparatus in accordance with claim 36, wherein a gas conductancepipe whose outer periphery is arranged spaced apart from the wall of themixing chamber is arranged in the mixing chamber.
 64. The apparatus inaccordance with claim 63, wherein at least one flow conductance elementis arranged between the outer periphery of the gas conductance pipe andthe wall of the mixer chamber.
 65. The apparatus in accordance withclaim 63, wherein at least one flow conductance element is provided thatis arranged in the gas conductance pipe or that at least sectionallyprojects into the gas conductance pipe.
 66. The apparatus in accordancewith claim 65, wherein the flow conductance element is arranged betweenthe protective sleeve and the gas conductance pipe.
 67. The apparatus inaccordance with claim 63, wherein the protective sleeve projects atleast sectionally into the gas conductance pipe in the axial direction.68. The apparatus in accordance with claim 63, wherein the gasconductance pipe has a section that flares in the flow direction of thegas flow.
 69. The apparatus in accordance with claim 63, wherein the gasconductance pipe has a funnel-like inlet region and/or a constrictionwith a reduced cross-section and/or a curved section.
 70. The apparatusin accordance with claim 63, wherein the gas conductance pipe isarranged coaxially to the mixing chamber and/or to the protectivesleeve.